The study will examine the development of the neuronal components of the visual cortex (areas 17, 18 and 17-18 border region) of the monkey (M. nemestrina, M. fascicularis, M. mulatta) from late foetal to adult using the Golgi technique. The sequence of development of each neuronal type seen in the adult will be followed in terms of dendritic and axonal maturity and relative to the maturation of the thalamocortical projection. Correlative studies using the electron microscope are planned to relate the synaptic development of individual laminae with dendritic and axonal development observed by the light microscope. The object of these studies will be to provide a better understanding of the structural basis of cortical vision. To accomplish this we need to know: 1. Whether neurons appearing as distinct forms in the adult are recognizable throughout development or derive from common cell types at different developmental stages, 2. How the intrinsic interconnections become organized in relation to the developing thalamic, callosal and intracortical pathways, and 3. Which neuron populations mature independently of visual input and which are dependent upon it perhaps during a critical period of maturation. This would be achieved by parallel studies on animals visually deprived by eyelid suture soon after birth. This work should provide a morphological background to physiological studies on the developing and mature primate visual cortex. It will also provide a baseline for further morphological study of disturbance of binocular interaction induced by squint and enucleation.